CHEMICAL COMPOSITION OF MINERAL8. 79 



mtiinony, boron, columbium, tantalum, vanadium, gold. For 

 example, for arsenic there are the compounds As 2 S, As.S 3 , 

 A.s,0 3 , As,0 5 , etc. Another characteristic of these elements of 

 the hydrogen, sodium, chlorine, and arsenic groups is that the 

 number of equivalents of the acidic element in the compounds 

 into which they enter is, with a rare exception, odd, and of the 

 1, 3, 5, etc., series, and on this account they are called in 

 chemistry perissads / while the other elements, in whose com- 

 pounds their number is of the 1, 2, 3, etc. (or 2, 4, 6) series, 

 are called artiads. An apparent exception exists under the 

 artiads in the sesqui oxides, but this does not alter the general 

 character of the series. 



The facts above cited sustain the general statement that 

 Ca 3 , Mg 3 , Mn 3 , Zn 3 , Fe 3 , Al, Ee, Mn, have equivalent combin- 

 ing values, and hence in minerals often replace one another ; 

 and so also Ca, Mg, Mn, Zn, Fe, K 2 , Na,, Li 2 , H 5 , may replace 

 one another. Similarly, also, As 2 , or Sb 2 replaces S in some 

 minerals. 



"With reference to the classification of minerals the elements 

 may be conveniently divided into two groups: (1) the Acidic, 

 and (2) the Basic. The former includes oxygen and the ele- 

 ments which were termed the acidifiers and acidifiable elements 

 in the old chemistry. They are those which have been called 

 in miueralogy the mineralizing elements, since they are the 

 elements which are found combined with the metals to make 

 them ores, that is, to mineralize them. The basic are the rest 

 of the elements. The groups overlap somewhat, but this need 

 not be dwelt upon here. 



The more important of the acidic elements are the following : 

 oxygen, fluorine, chlorine, bromine, iodine, sulphur, selenium, 

 tellurium, boron, chromium, molybdenum, tungsten, phosphorus, 

 arsenic, antimony, vanadium, nitrogen, tantalum, columbium, 

 carbon, silicon. 



Again, among the compounds of these elements occurring in 

 tho mineral kingdom there are two grand divisions, the binary 

 and the ternary. The binary consist of one or more elements 

 of each of the acidic and basic divisions, and the ternary of on8 

 or more elements of each of these two classes, along with oxy- 

 gen, fluorine, or sulphur as a third. The binary include the 

 sulphides, arsenides, chlorides, fluorides, oxides, etc., and the 

 ternary the sulphates, eliminates, borates, arsenates, phospliates % 

 silicates, carbonates, etc., and also the sulph-arsenites and sulph- 

 antimonites, in which a basic metal (usually lead, copper, sil- 

 ver) is combined with arsenic or antimony and sulphur. 



